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Author Topic: What force is causing the universe expansion to be accelerating  (Read 3565 times)

Offline percepts

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If the universe is expanding at an accelerating pace then I presume there is force causing the acceleration. And if it is expanding in all directions at an accelerating pace then is that force coming from the centre of the universe or it it being attracted out by some force outside of the universe. Do we even know what this force is or is there another reason for the acceleration.


 

Offline Pmb

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If the universe is expanding at an accelerating pace then I presume there is force causing the acceleration. And if it is expanding in all directions at an accelerating pace then is that force coming from the centre of the universe or it it being attracted out by some force outside of the universe. Do we even know what this force is or is there another reason for the acceleration.
Nobody knows what's causing it. The name that's given to the source is Dark Energy whatever that is. It's modeled using what's called a cosmological constant and negative pressure. For details about how these fit together please see the chapter in cosmology in Exploring Black Holes - Second Edition. It's online at
http://www.eftaylor.com/exploringblackholes/Cosmos110410v1.pdf

Dark energy contributes to 73% of the mass-energy of the universe. One possibility is vacuum energy which has been shown to be equivalent to a cosmological  constant. Another source could be negative pressure.
« Last Edit: 04/04/2013 21:03:03 by Pmb »
 

Offline Ethos_

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 Do we even know what this force is or is there another reason for the acceleration.
That's the 64 thousand dollar question my friend. As the previous poster has said, they are calling it dark energy. But the proof for that is still awaiting evidence. And I would add another question to the mix if I may.

Is this expansion universal or may it only be a local event?

I'll assume that scientists have concluded that it must be universal so I'd be interested in knowing the facts that have lead them to this decision.

A simple observation if I may; The reason they call it Dark Energy is because they really don't understand it yet. I would personally think it more proper to deem this as; An Hypothesis and not yet equal to a theory.
 

 

Offline yor_on

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The funny thing about space is that we don't really know why it exist, or we do know, as without it there would be no universe to measure. But as to its nature we do not know. We expect it to contain energies, and 'bosons' as the Higg particle/field, but if that also is 'space' is another thing.
 

Offline Ethos_

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The funny thing about space is that we don't really know why it exist,
Truly yor_on, but we surely have a multitude of opinions concerning how it came into existence. The favorite at present would of course be, the Standard Model with the Big Bang at it's Genesis. With Brane theory suggesting a collision of dimensional fabrics, the Cyclical version, and the Steady State Model, one has a seemingly inexhaustible number of choices from which to choose. But as you mentioned, why is it expanding and what the true nature of space really is, that's the enigma we face.

But why space is here is likely more of a philosophically defined question. At least for the present and foreseeable future. I suppose one could dismiss it by saying: "We observe space as one of an infinite variety of possible quantum fluctuations." But to answer, "Why is the expansion accelerating?" is not so easy a task. 
 

Offline percepts

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OK thanks, so I have an idea of the limits to human knowledge about the universe. We're not sure where it came from and we don't know where it's going. Lots more research to be done...
 

Offline yor_on

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Yes Ethos, myself I think of it as being modeled from gravity, being the 'metric' of space, defining its 'bumps and jumps' :) Then again, maybe 'space' have a existence without 'gravity' too? Or maybe they are the same? Meaning that it can't exist without it. Think of a 'flat space' without gravity, is it three dimensional?
 

Offline Pmb

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You might find this interesting

Observables and unobservables in dark energy cosmologies
 http://arxiv.org/abs/1210.0439

I haven't read it yet though.

 

Offline yor_on

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But it also goes back to 'motion', as that is what we use to define 'distances', in a indirect way. We find things able to move in a 'space', and so we define both a distance, as well as a 'time', taken. Motion tells us that it happens under time, and that involves a displacement in the room. but under relativity it becomes local definitions.
 

Offline yor_on

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Lots of mathematics in that one Pete :)
Inflation seems real enough to me, although, maybe it is just the regime we live in and under defining both a distance and a time. Our universe a conjurer.
 

Offline Ethos_

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Motion tells us that it happens under time, and that involves a displacement in the room. but under relativity it becomes local definitions.
Interesting that you would mention the relationship between relativity and defining a local event. Leonard Suskind, a well known and respected cosmologist, has proposed what he calls; The Holographic Universe. He suggests that all the information in the universe is entangled with a two dimensional sphere at the edge of the universe. This suggests an entirely different meaning for the word local. If his model is correct, and we consider what this does to the meaning of the word local, we must also consider what this does to the meaning of expansion. Please understand, I'm not suggesting an answer here, I'm just making an observation.

Here's a video that should explain his theory for those interested:

« Last Edit: 06/04/2013 01:51:09 by Ethos_ »
 

Offline Ethos_

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BTW, I misspelled his name, it should be Susskind.
 

Offline yor_on

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Maybe, maybe not. A holographic universe don't need observer dependencies as I think, just as a ordinary hologram should present you with a same measure between points. So does it fit relativity? Maybe it is possible to adapt it, but then you also need to prove why it would choose such a complicated way of describing it.
 

Offline yor_on

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the holographic universe did not come as a answer to relativity. It came as a possible answer to black holes and entropy/information getting lost, as I gather. And ultimately as a quantum mechanical answer. But that we today all are very interested in QM does not invalidate relativity.
 

Offline Ethos_

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the holographic universe did not come as a answer to relativity. It came as a possible answer to black holes and entropy/information getting lost, as I gather. And ultimately as a quantum mechanical answer. But that we today all are very interested in QM does not invalidate relativity.
You're correct in your assessment yor_on, Susskind's theory does not invalidate relativity but he does make a connection between Black Hole physics and the nature of the universe. If you've watched the video, you'll notice how he compares conservation of information at the Scharzchild radius to similar conditions at the spherical boundary of our universe. And he makes a case for both being similar to how information is stored on a Holographic image.

Many scientists have drawn comparisons between Black Hole physics and the speculated nature of our universe. This is not to say however that our Universe and a Black Hole are equivalent.  Nevertheless, the expansion we observe may be in some way linked to these similarities.
« Last Edit: 06/04/2013 14:52:02 by Ethos_ »
 

Offline yor_on

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I have my own ideas there, more resembling strings than anything else. Using those it all becomes a question of 'information' and 'relations'. It's very theoretical (meaning hand waving:) though and ignore our definitions of dimensions, as being constructs we gain by living under our regime defining a measurable universe. But using it I don't need to define information solely from the point of what we measure, although I still would need to define how we can find our regime to answer the conservation laws we expect to exist. But then I think of fractal behaviors.
 

Offline Ethos_

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I have my own ideas there, more resembling strings than anything else.

Interesting, and BTW, Susskind was one of the pioneers in string theory. Could you define for us how you see fractals involved in this question of expansion?
 

Offline yor_on

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A fractal behavior is to me something that is 'self like', at/over different scales. It's a over-simplification of course, and there are different types of fractals. But if you imagine all of it, what we can measure and what we can not, as consisting of relations, then, possibly, you could assume some fractal pattern related to the scales we observe. But I'm definitely not sure of any of this. You could also go out from lights constant, and, again possibly, define it such as this constant should be existent for all of it, what we can measure and that we can't. Then that might bind it together, with what we can measure on being a fractal pattern, coming from what we can't measure on. If you ignore dimensions and assume that it all comes down to relations, communicating through a constant that also becomes a ultimate 'clock'. Then what we can see and infer can still only be a part of 'what exist', and exist simultaneously, hopefully :) under one and the same arrow for it all. Because I believe in 'time' and its arrow, and I believe in 'c' as a constant. They are my archetypes if you like, from where I want to go out. But you have to forget about 'dimensions' to make it work, and replace them with paths defining relations.
 

Offline Ethos_

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A fractal behavior is to me something that is 'self like', at/over different scales. It's a over-simplification of course, and there are different types of fractals.

If I understand you correctly, this scaling up may be similar to something like what happens to the surface of a pond when the water freezes over it's surface. This of course would be as you say; "greatly over simplified" but something most of us can relate in our everyday experience.
 

Offline yor_on

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It goes back to how complexity can come from the simple Ethos, for me that is :) And there I don't know anything that seems to work better than fractals, maybe a holographic universe can be described in those terms too though. But fractal patterns can be found everywhere it seems, in nature and in cosmos.

Also, replacing the concept dimensions with paths are very important to me. And paths can also be described as 'degrees of freedom', with a few degrees defining our universe (4), although only one being a constant, the other being constructs.
 

Offline yor_on

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You can think of it this way. From locality there are two constants assumed. The arrow, becoming 'c'. they locally becomes the same everywhere. Then we have the other three, they can also locally be defined as non changing relative your ruler and clock. But assuming there are paths existing that we can't measure on they must still be constructs. The arrow is 'c' to me, and that can't be a construct, the arrow and 'c' goes hand in hand. And it's all terribly cerebral, meaning that it won't fit what we see in our daily lives, only as an idea for that we can't see.
=

Because going out from locality solely you will be forced to look at the universe differently. There are no choice, unless you want to make it extremely complicated. From locality each position has a unique description of all other locations in space and time. And what joins them are 'frames of reference', and 'c', and a locally same arrow. if you accept that you can exchange any definition of a length, height, and width with 'distance', and then think of how that 'distance' according to relativity can shrink for you, locally measuring, then you can see how I think there.
« Last Edit: 06/04/2013 22:58:31 by yor_on »
 

Offline Ethos_

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And it's all terribly cerebral, meaning that it won't fit what we see in our daily lives, only as an idea for that we can't see.
But of course, and I am familiar with the GR to a certain degree. But the idea of fractals growing from a common source is rather new to me. But I do see where this could explain a few things. I have some information that I would like to share, but I think it appropriate to only do that via private message. I don't wish to hi-jack this thread with another issue my friend. If you like, I would like to share this information with you. If you think that would be OK, just say so and I'll send you a PM.
 

Offline yor_on

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Well, those last ideas may not be fitting here either, new theories should be the correct place, although I sometimes wish TNS had called that place 'New hypotheses' instead :) A theory demands more than words. But I can at least prove some of them to my own satisfaction. Fractals though, are very tricky, although they must bear a relation to the universe we see. I wonder how it would fit a description of a holographic image? And sure, if you think your thoughts are of main stream definitions feel free to write :)
 

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